The present invention relates to a CPU cooling device using a thermo-siphon for cooling, in particular a central processing unit (hereinafter referred to as a xe2x80x9cCPUxe2x80x9d) used in a desktop type computer.
Today, computers are becoming smaller and to be operated at higher speed than ever. Electronic circuits of the CPU are more integrated and produce more heat. Accordingly, methods to improve cooling capacity of the CPU have been desirable.
Conventionally, CPU is cooled by drawing ambient air into the computer cabinet by using fans and ventilation systems and circulating the air over the CPU. Amount of heat per unit area produced from CPU becomes larger, it requires either to increase air flow circulating over the CPU or to dispose cooling fins in order to increase heat-transmission areas. However, increase of air flow causes a larger consumption of electric power and more noise by the fans, and an increase of spaces for air flow passages around the CPU. Further, disposing cooling fins requires additional spaces and prevents size reduction of the computers. To blow pre-cooled air against the CPU is also available. However, as it needs devices for pre-cooling air, it increases both manufacturing and operating cost of the computer as well as their size.
Briefly, an object of the present invention is to provide an improved cooling device using a thermo-siphon for cooling CPU. The cooling device saves operating cost, consumes less electricity, and reduces operating noises while enhancing cooling capacity of the CPU.
More specifically, first object of the present invention is to provide an improved cooling device using a thermo-siphon which efficiently absorbs heat generated from the CPU from a restricted space. Second object is to provide a cooling device using a thermo-siphon which needs no external power such as a pump or the like for circulating the refrigerant. Third object is to provide a cooling device using a thermo-siphon which efficiently take enough heat out of CPU in such cases that the CPU is planed to run in relatively low temperature, that the CPU produces much heat, and that the space for the condenser is small.
In order to solve these problems, first feature of the present invention comprises an evaporator disposed in contact with the CPU and a condenser located above the evaporator. The evaporator is a hollow vessel having an inlet port of a refrigerant and an outlet port thereof. The condenser has an inflow portion of a_vaporized refrigerant located at an upper portion thereof and an outflow portion of a liquefied refrigerant located at a lower portion thereof. The inlet port of the refrigerant and the outflow portion of the liquefied refrigerant are connected by a liquid flow channel, while the outlet port of the refrigerant and the inflow portion of the vaporized refrigerant are connected by a vapor flow channel. A predetermined amount of refrigerant fills a flow circulating channel comprising the evaporator, the condenser, the liquid flow channel, and the vapor flow channel. The refrigerant absorbs heat from the CPU in the evaporator to be evaporated, ascends through the vapor flow channel, enters into the condenser, radiates the heat in the condenser to be liquefied, flows down through the liquid flow channel, and returns to the evaporator.
The condenser refers to all means having a structure with an inflow portion located at its upper portion into which the vaporized refrigerant flows, and an outflow portion located at its lower portion from which the liquefied refrigerant flows out, and the vaporized refrigerant radiates heat to the outside in the portion of the flow channel between the inflow portion and the outflow portion. The refrigerant includes all refrigerants which operates in the states of liquid and gas in the flow channel and has the property of evaporating (being gasified) from liquid to vapor at temperatures lower than allowable temperatures of the CPU.
By configuring the invention in this manner, heat from the CPU is absorbed into the liquefied refrigerant having a higher heat transmission rate than air, and the absorbed heat is converted into the evaporated heat of the refrigerant. The vaporized refrigerant ascends through the vapor flow channel, flows into the condenser from the inflow portion of the vaporized refrigerant, and radiates heat in the condenser to be liquefied. The liquefied refrigerant moves by its own weight toward the outflow portion of the liquefied refrigerant, while gradually increasing the flow rate in the condenser. Then the liquefied refrigerant flows down through the liquid flow channel from the outflow portion and returns to the evaporator.
Accordingly, heat from the CPU can be efficiently absorbed from the small surface of the CPU without cooling fins and the like. Further, as the condenser may be positioned away from the CPU, spaces for the flow passage of the cooled air or the like is not required around the CPU. Therefore, wiring of parts associated with CPU can be more integrated and the structure of the periphery of the CPU can be decreased. Furthermore, as the refrigerant can be circulating continuously through the flow channel without external power such as a pump or the like, energy conservation and noise reduction can be achieved.
The present invention employs a configuration of a thermo-siphon in which the evaporator and the condenser is connected by two flow channels; a vapor flow channel and a liquid flow channel. It enables to improve the heat absorption effect at the evaporator and the heat radiation effect at the condenser.
Another configuration is possible, in which an evaporator and a condenser are connected by a thick single flow channel. In the latter configuration, a vaporized refrigerant ascends through the flow channel by convection and radiates heat in a condenser, while a liquefied refrigerant flows down by its own weight through the same flow channel and returns to the evaporator located at the lower position. As the ascending vaporized refrigerant comes into contact with the descending liquefied refrigerant in the single flow channel, there happens heat exchanges between the liquefied refrigerant and the vaporized refrigerant inside the flow channel. Consequently, as the temperature of the liquefied refrigerant rises, both the absorbed heat from the CPU and the radiated heat at the condenser are decreased. In contrast, in the configuration employed in the present invention where the flow channel is divided into a vapor flow channel and a liquid flow channel, all the vaporized refrigerant can be used to radiate heat in the condenser, while all the liquefied refrigerant can be used to lower the temperature of the CPU in the evaporator, thereby improving the effect of absorbing heat from the CPU.
A second feature of the present invention is to provide the CPU cooling device according to the first feature, wherein said condenser comprises a flow channel and a heat-radiating fin. The flow channel has the inflow portion of the vaporized refrigerant located at the upper portion of the condenser and the outflow portion of the liquefied refrigerant located at the lower portion thereof. The heat-radiating fin is disposed in contact with the flow channel. The flow channel can be configured in being straight, being folded back a plurality of times on the same level, or being spirally wound a plurality of times. By configuring the present invention in this manner, a CPU cooling device with small and low cost condenser can be realized.
Third feature of the present invention is to provide the CPU cooling device according to the first or second feature, wherein the flow area of the liquid flow channel is smaller than that of said vapor flow channel. By configuring the present invention in this manner, reverse flows of the vaporized refrigerant through the liquid flow channel can be prevented. Consequently, circulation of the refrigerant improves to increase the amount of heat absorbed from the CPU.
Fourth feature of the present invention is to provide the CPU cooling device according to any one of the first to third features, wherein the liquid flow channel is disposed inside of the vapor flow channel. As this configuration saves spaces for disposing the flow channel, arrangement of the flow channel is more facilitated.
Fifth feature of the present invention is to provide the CPU cooling device according to the first to fourth features, wherein the refrigerant is pre-pressurized and sealed. By configuring the invention in this manner, the vaporized refrigerant having the same mass circulate in narrower flow channel area. As spaces for arranging the flow channel is decreased, arrangements of the flow channel are more facilitated. Further, the evaporating temperature of the refrigerant can be altered by changing the operating pressure of the refrigerant to cope with allowable temperatures of the CPU.
Sixth feature of the present invention is to provide the CPU cooling device according to the first to fifth features, wherein the condenser comprises a flow channel and a Stirling refrigerator. The flow channel has the inflow portion of the vaporized refrigerant located at an upper portion of the condenser and the outflow portion of the liquefied refrigerant located at a lower portion thereof. The flow channel is disposed in contact with a heat sink portion of the Stirling refrigerator. The Stirling refrigerator can be light and small-sized while efficiently working in low electric power.
The Stirling refrigerator means a known-art device in which an external combustion engine is modified to a refrigerating device to provide a heat sink function by giving an external power. By configuring the invention in this manner, it is possible to efficiently cool the CPU, even though it generates larger amount of heat. In general, amount of heat from the CPU is greater, more heat transmission area of the condenser for radiating heat of the vapor is required. However, there are found situations where small spaces are available for a heat transmission area. In such situations, the Stirling refrigerator can provide enough heat radiating capacity.